Note : Angela Stickle is an impact simulation expert for DART mission
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Title - Impact modeling for the Double Asteroid Redirection Test (DART) mission
By - Emma Rainey et al, 2020 (Angela Stickle), PDF link
Summary - Rough estimates for impact crater : 2 m for high-strength & 20+ m for a low-strength case (this is not explicitly mentioned but obtained from paper 11 here, Masatoshi Hirabayashi et al, 2022). The results of this study show that for realistic combinations of asteroid material properties, the DART impact would be expected to produce a β between 1.5 and 2.
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By - Angela Stickle et al, Sept 2022 (Sabina Raducan)
Summary -
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Title - Modeling momentum transfer from the dart spacecraft impact into the moon of Didymos
By - Angela Stickle et al, 2015 (PDC2015)
Summary - final crater size between 8m and 17 m.
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Angela Stickle tweet, 2019, crater diameter of 15 m
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Angela Stickle et al, 2015 (No. 3)
Modeling momentum transfer from the dart spacecraft impact into the moon of Didymos
Crater scaling rules can be used to estimate the amount of ejecta expected to escape both the moon and the binary system following impact as well as the final crater size.
The most likely scenario for the moon’s material properties is that of a highly porous rock that possesses some shear and compressive strength, but little tensile strength. This is because the moon of a small binary asteroid is likely the result of re-accreting regolith that was shed by the parent binary to produce a loosely bound, highly porous moon; the material resistance to deformation will then mostly depend on the confining pressure from the self-gravity holding the aggregate together.
For the case of the DART impact, in order for the cratering process on Didymos’ moon to be gravity dominated, the effective strength of the moon would have to be 4 Pa.
This is probably unreasonably low and the DART impact into the moon of Didymos is likely to be a strength-dominated event.
We consider a range of possible material strength values for the moon between 0 and 18 MPa (representing unconsolidated, strengthless sand or hard rock, respectively).
For the chosen range of strength values and scaling parameters from [1], DART impact would form a crater between 8 m (for hard rock) and 114 m (for strengthless sand) in diameter. These same craters would have a cumulative mass of escaping ejecta of 10^4 kg and 10^6 kg.
The most likely range of scenarios (i.e., strength values and scaling parameters), however, result in a final crater size between 8m and 17 m, and a cumulative mass of escaping ejecta between 10^4 and 10^5 kg.
Impact simulations used the CTH hydrocode from Sandia National Laboratories.
Because the physical properties of the Didymos system are not well known, we examined a variety of target properties (e.g., material strength and porosity) and impact scenarios to constrain the expected results of the DART impact.
For “realistic” material properties (sand or weak/soft rock) the analytical models predicted crater diameters between 8 and 17 m.
Weak rock : 12 m crater (yield strength of 7.6 MPa)
Sand : 8 m crater (yield strength of 1 MPa)
For equivalent impacts (90°, through the COF), the range predicted by these CTH simulations is 6–15 m, a difference of 12–25% from the analytical predictions.
β = 3.8 for competent rock (table 2)
For fully dense, competent, strong rocks, we calculate values for β between approximately 3.8 and 5.5
NOTE : Ryugu SCI impact took place on April 5, 2019
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